Existing hospital beds have a fowler portion which supports the head and upper torso of a patient and which can be pivoted from a horizontal position upwardly to various inclined positions. A common drive arrangement for the fowler includes a reversible electric motor which can rotatably drive a threaded shaft extending lengthwise of the bed, a nut which engages the threaded shaft and is held against rotation so that the nut moves axially along the shaft in response to rotation of the shaft, and a linkage which couples the nut to the fowler portion so that the fowler portion pivots in response to axial movement of the nut in order to alter the inclination of the fowler portion.
When a patient experiences a sudden trauma such as a heart attack while the fowler portion is in the inclined position, it is medically important that the fowler portion be pivoted downwardly as quickly as possible to an approximately horizontal position, so that appropriate therapy such as cardio-pulmonary resuscitation (CPR) can be administered. Also, there are times when the fowler must be operated without electrical power, for example to shorten the effective length of the bed so that it will fit into an elevator during patient transport. However, in most existing fowler drive arrangements, the threaded shaft has a relatively fine pitch and is rotated at a slow to moderate speed in order to permit slow and gentle movement of a patient during normal operation. In order to move the fowler portion to its horizontal position substantially more rapidly than is possible by using the electric motor, manually operable quick release arrangements have previously been developed to allow selective interruption of the driving connection between the rotating shaft and the fowler portion. One example of such a known quick release mechanism is disclosed in Peck U.S. Pat. No. 4 559 655. While this known mechanism has been generally adequate for its intended purposes, it has not been satisfactory in all respects.
For example, the quick release mechanism in this known apparatus includes a relatively bulky coupling mechanism which reciprocally moves lengthwise along the threaded shaft with the nut, and an appropriate clearance space must be provided along the entire range of movement of the nut to allow movement of this bulky coupling arrangement. Consequently, this known fowler drive mechanism is not very compact and requires the allocation of a relatively significantly amount of space beneath the patient support, which in some situations is undesirable or impractical.
An object of the present invention is to provide an improved quick release mechanism for a motor-driven fowler which permits the entire fowler drive arrangement to be relatively compact.
A further object provides such a mechanism which can be quickly and reliably released and re-engaged, and which requires little or no maintenance over its normal operational lifetime.